The present invention is directed toward printed circuit boards (PCBs) and the like. These circuit boards typically include large numbers of electronic devices which are commonly surface mounted and also additional components which may be present in the form of active layers within each PCB. The requirements for the devices and components in such printed circuit boards are subject to conventional electronic design restraints.
More specifically, many of the surface mounted devices and other components on such PCBs commonly require coupling with individual resistors in order to achieve their desired function.
The most common solution to this problem in the prior art has been the use of individual resistors as additional surface mounted components on the PCBs. Design of the PCBs has further required the provision of through-holes in order to properly interconnect the resistors. In this regard, the resistors may be interconnected between any combination of surface devices or components or active components or layers formed on or within the PCBs.
Accordingly, the provision of such resistors has increased the complexity of the PCBs and at the same time either decreased the available surface area of the PCBs for other devices or else resulted in an overall increase in the size of the PCBs to accommodate necessary surface devices and components including resistors.
A more recent solution to this problem in the prior art has been the provision of planar resistors preferably formed on internal layers of the PCBs in order to replace prior art surface mounted resistors as described above while making surface portions of the PCBs free for other uses.
This concept involved the replacement of surface mounted or discrete resistors by resistors formed on layers arranged either on or within the PCBs.
Although such planar resistors provide advantages in certain applications over discrete surface mounted resistors, they have still tended to result in relative increases in the complexity and space demands on the PCBs. For example, if the planar resistors are formed on a surface layer of the PCB, it is of course possible to arrange an active surface device over the resistor. However, that surface portion of the PCB occupied by the planar resistor must be dedicated to the planar resistor itself. Accordingly, that portion of the board is not available for mounting pads, through-holes or the like. At the same time, it is also necessary to provide conductive couplings for interconnecting the surface formed planar resistors in order couple them with active devices or components in the PCBs. Here again, plated through-holes have commonly been employed for this purpose and further increase complexity and space demands in the PCBs.
Planar resistors of the type described above have also been formed on internal layers or planes of the PCBs. Such a configuration permits the use of standard subtractive PCB techniques, for example, to produce conductor patterns and resistor elements suited for high speed and high density circuit applications. However, even with the planar resistors being formed on internal layers of the PCBs, it is still necessary to provide plated through-holes or other conductors extending in a Z direction through the PCBs in order to provide the necessary couplings for the planar resistors with various surface mounted devices or components in the PCBs.
Accordingly, there has been found to remain a further need for improvements in the provision of resistors for various devices and components in PCBs.